Display screen or portion thereof with a graphical user interface



The sole FIGURE shows a display screen or portion thereof with a graphical user interface.

The outermost broken line represents a display screen or portion thereof and forms no part of the claimed design. The remaining broken lines represent portions of the graphical user interface that form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 